The lamb was slain from the foundation of the world, so salvation was always possible before the cross
Even those who died before Christ’s ministry had the gospel preached unto them:
“…for this cause was
the gospel preached also to them that are dead, that they might be judged according to men in the flesh, but live according to God in the spirit.” (1 Peter 4:6)
“For Christ also hath once suffered for sins, the just for the unjust, that he might bring us to God, being put to death in the flesh, but quickened by the Spirit:
By which also he went and preached unto the spirits in prison; Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water.” (1 Peter 3:18-20)